Abstract:

In order to establish a rapid DNA molecule identification system of lettuce varieties,8 lettuce varieties of different types with significant morphological differences were chosen and used for preliminary primer-screening,and 81 pairs of primary primers were selected from 245 pairs of primers by polyacrylamide gel electrophoresis. Labeled with fluorescence at 5' end of upstream,the 81 pairs of primary primers were re-screened with 90 lettuce varieties by capillary electrophoresis,and 22 pairs of core primers were finally screened out. The corresponding reference samples for each of the core primers were also selected according to the size of amplified fragments and a SSR fingerprint database of 233 varieties was constructed based on these core primers. The results showed that 22 pairs of core primers detected a total of 269 alleles in 233 varieties. For each pair of primers,the detected alleles ranged from 4 to 22,with an average of 12.23,and the PIC value ranged from 0.37 to 0.89,with an average of 0.73. Cluster analysis showed that 233 varieties were divided into two major groups of stem lettuce and leaf lettuce. Among the leaf groups,crisphead lettuce cluster into a group,half-hitch lettuce tended to cluster into a group,and looseleaf lettuce was difficult to cluster into a group. 15 varieties in 6 groups with no difference in SSR markers were compared in a field trail. 3 pairs of varieties with no significant morphological differences were determined as the same and other varieties from different groups were determined as similar varieties because of a few morphological differences. Thus,the result of DNA clustering was basically in agreement with that of the field morphological classification. In addition,24 varieties in 8 groups with the same name can be distinguished by the molecular markers. In conclusion,a fingerprint database of 233 lettuce varieties was constructed based on the 22 pairs of core primers and a variety identification system for stem lettuce and leaf lettuce was established,which could be used for rapid identification of lettuce varieties and germplasm resources,genetic diversity analysis and similar variety selection in DUS testing.

Key words: Lettuce, Variety identification system, SSR markers, DNA fingerprint, DUS testing